The "cache" command:

Usage: fossil cache SUBCOMMAND

Manage the cache used for potentially expensive web pages such as
/zip and /tarball.   SUBCOMMAND can be:

   clear        Remove all entries from the cache.

   init         Create the cache file if it does not already exist.

   list|ls      List the keys and content sizes and other stats for
                all entries currently in the cache.

   status       Show a summary of the cache status.

The cache is stored in a file that is distinct from the repository
but that is held in the same directory as the repository.  The cache
file can be deleted in order to completely disable the cache.